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Two relatively uncommon diseases of apples, lenticel infection and bitter rot, show up in the stressful weather conditions of 2012 in Michigan.

The hot and dry weather conditions during 2012 have
not only reduced crops in Michigan, but caused somewhat uncommon diseases to occur
when trees are under these stresses. One type of disease that has shown up on
apples this season appears as numerous small, dark spots, arranged somewhat
uniformly on the skin surface. Initially, the spots are quite shallow, but over
time they often become wider and deeper into the fruit. These infections are
more common on the side of the fruit receiving direct sunlight. Isolations from
these tissues show a range of fungi such as Cladosporiumand Alternaria; all of these fungi
are generally considered to be weak.

We hypothesize that the combined heat and
sunlight weakened the lenticels of the skin, allowing the weak pathogens to
colonize the area. Lenticels can also be weakened by an extended dry period
followed by rain, a situation that will also cause peach skin to split.
Lenticels that "split" appear as enlarged and roughened lenticels on
fruit at harvest.

Lenticel infections of Honeycrisp fruit.

No spray program is particularly effective
against lenticel spot although routine calcium sprays help to strengthen fruit
tissue and Surround (kaolin clay) applications have been shown to help reduce direct
sunlight damage to apple fruit.

Bitter rot, caused by the closely related fungi Colletotricum gloeosporiodes and Colletotrichum acutatum, can also show
up in hot years. Although bitter rot is well known in warmer, humid apple
growing regions such as the southeast United States, the disease is rare in
Michigan. The symptoms are more common on light or bicolored fruit such as Empire,
Mclntosh, Sunrise, Paulared and Jonagold. Bitter rot spots usually appear on
the side of the apple directly exposed to the sun. Lesions are light to dark
brown, flattened, and may have a pink, slight orange to light tan mass of
spores.

Bitter rot
symptoms of apple fruit. Flattened and concentric lesions
are characteristic of
this disease.

Captan or Flint during late July and August are effective
for controlling bitter rot. Topsin
M is not effective for bitter rot control. The
disease overwinters in dead limbs and mummified fruit. If bitter rot reoccurs in an apple block, more
thorough dormant pruning is recommended. Large diameter wood from pruning should
be removed from the orchard to minimize the spread of the disease.

November 10, 2016 | Erin Lizotte | Unseasonably warm weather and continued grass growth may be hiding a significant amount of rodent activity. Growers are advised to scout carefully and consider mowing tall undergrowth one more time before snow falls.

November 9, 2016 | Meghan Milbrath | Heroes to Hives aims to support military veterans by teaching the profession of beekeeping. Applications to attend the program can be submitted through Dec. 15, 2016.